Signal Processing Device and Signal Processing Method

ABSTRACT

A problem that when signal input/output is conducted in an analogue signal format between two portions processing digital signals, the dynamic range becomes inadequate due to error variations of signal levels of an internal D/A converter and A/D converter is solved. In a gain setting, firstly the magnitude relation is so set that a minimum value in a signal level error variation range of a D/A converter ( 12 ) in a front stage DSP ( 1 ) is greater than a maximum value in a signal level error variation range of an A/D converter ( 21 ) in a rear stage signal processing block. Secondly, in a state that a signal having the level handled as a predetermined maximum value in the DSP ( 1 ) is inputted to a first GCA ( 13 ), the gain value of the first GCA ( 13 ) is so set that the level of a signal S 5  is the maximum in a range of below a prescribed value Vdr. Thirdly, the gain value of a second GCA ( 24 ) is so set that the level of the signal S 5  is the maximum in a range of equal or less than a prescribed value.

TECHNICAL FIELD

The present invention relates to a signal processing device and a signalprocessing method that mainly set a gain for, for example, a videosignal, and the like.

BACKGROUND ART

In the field of equipment including an image display apparatus thatrequires video signal processing, the video signal processing isgenerally executed by digital signal processing due to widespread use ofchips and devices called DSP (digital signal processor).

FIG. 6 shows an arrangement of an image display apparatus having a LCD(liquid crystal display) as a display device as an example of equipmentfor executing video signal processing by the DSP provided therewith.

A DSP 1 shown in the figure is composed of, for example, one chip or onedevice and executes necessary signal processing to an input digitalvideo signal by a signal processing unit 11 formed in the chip or thedevice. The signal processing executed here is digital signalprocessing. The DSP 1 outputs the digital video signal, which issubjected to the signal processing by the signal processing unit 11, tothe outside from a terminal T1 after it is converted into an analogvideo signal by a D/A converter 12.

In this case, the terminal T1 of the DSP 1 is connected to a terminal T4of an LCD drive circuit 2 composed of one device likewise, for example,the DSP 1, thereby the analog video signal output from the terminal T1of the DSP 1 is input to the LCD drive circuit 2 through the terminalT4.

The LCD drive circuit 2 creates a drive signal for driving an LCD 3 fordisplay based on the analog video signal input thereto and outputs thedrive signal from a terminal T5. In this case, the terminal T5 isconnected to a terminal T6 of the LCD 3 as a display device, and thedrive signal is input to the LCD 3 from the terminal T6.

The LCD 3 drives a pixel cell in response to the drive signal inputthereto. With this operation, the LCD 3 displays an image according tothe video signal.

Incidentally, it is assumed that the image display apparatus arranged asshown in, for example, FIG. 6 must be modified so that a novel videosignal processing function can be added thereto. It is firstcontemplated to remake the DSP 1 to cope with the modification. However,remaking it takes a cost such as development cost, a manufacturing cost,and the like. Accordingly, when the modification is not executed on alarge scale, there is a disadvantage in that an effect such as an appealto users and the like obtained by the modification does not worth thecost increased by remaking the DSP 1.

In this case, there is employed a method of mounting an external circuit(chip, device) that corresponds to the novel video signal processingfunction. Further, when the external circuit is composed of an analogcircuit for executing analog video signal processing, a disadvantagearises in that a circuit size is increased and dispersion and the likeof a signal level are also increased. Thus, it is preferable to arrangethe external circuit so as to execute digital signal processing.

FIG. 7 shows an image display apparatus on which mounted is an externalcircuit (chip, device) arranged to execute the digital signal processingas described in the latter method. Note that, in FIG. 7, the sameportions as those in FIG. 6 are denoted by the same reference numerals,and the explanation thereof is omitted.

In the image display apparatus shown in the figure, a signal processingblock 4 as an external digital signal processing circuit (chip, device)is interposed between a DSP 1 and an LCD drive circuit 3.

Since a terminal T2 of the signal processing block 4 is connected to aterminal T1 of the DSP 1, an analog video signal is input to theterminal T2 after it is subjected to signal processing by the DSP 1.

As an internal arrangement of the signal processing block 4, first, theanalog video signal input through the terminal T2 as described above isconverted into a digital video signal by an A/D converter 21 so that itcan be subjected to digital signal processing internally. Then, videosignal processing corresponding to a specific function is executed bythe digital signal processing executed by a signal processing unit 22.Then, the digital video signal, which is subjected to the signalprocessing as described above, is converted into an analog video signalby a D/A converter 23 so that it can be input to an LCD drive circuit 2and then output from a terminal T3. The terminal T3 is connected to aterminal T4 of the LCD drive circuit 2, thereby the analog video signalis input to the LCD drive circuit 2 (refer to Japanese Unexamined PatentApplication Publication No. 10-336547).

Incidentally, the signal processing block 4 in the image displayapparatus shown in FIG. 7 includes cells of the A/D converter 21 and theD/A converter 23 so that it cope with an input/output of the analogvideo signal while executing the video signal processing therein by thedigital signal processing. Further, in the image display apparatus shownin FIG. 7, a cell of a D/A converter 12 is also included in the DSP 1.Accordingly, a system of the image display apparatus shown in FIG. 7 hasthe cells of three sets of the A/D converters and D/A converters in itsentirety.

As an actual matter, it is known that the cells of the A/D convertersand the D/A converters of these devices have dispersion (error) ininput/output signal levels (data values in a digital signal).

Dispersion of the cells of the A/D converters and the D/A converters isguaranteed so that it is within a predetermined range. However, when thenumber of the cells of the A/D converters and the D/A convertersconnected to each other in series increases as shown in FIG. 7, an errorof an overall data value (signal level) increases. When the errorincreases as described above, an original dynamic range cannot beeffectively utilized because, for example, a data value (level) tends tooverflow (excessively input) or a signal level is made too small.

What has been described above will be explained with reference to FIGS.8A, B, and C.

First, FIG. 8A shows a case in which the dynamic range (maximum outputlevel) of the D/A converter 12 in the DSP 1 is the same as the dynamicrange (maximum input level) of the A/D converter 21 of the signalprocessing block 4.

The data value of an input signal S1 (output from a signal processingunit 11 in FIG. 7) of the D/A converter 12 is set to a level Ldr thatcorresponds to the dynamic range DR of the A/D converter 21. Then, asignal S2, which is obtained by converting the input signal S1 into ananalog signal by the D/A converter 12, has the level Ldr because thedynamic range of the D/A converter 12 is the same as that of the A/Dconverter 21.

That is, this case is in such a state that an ideal dynamic range issecured in which an input signal having a maximum value is kept as it iswithout overflowing.

In contrast, FIG. 8B shows a case in which the dynamic range (maximumoutput level) of the D/A converter 12 in the DSP 1 is larger than thedynamic range (maximum input level) of the A/D converter 21 of thesignal processing block 4 as a relation to the dispersion of error.

In this case, since the D/A converter 12 has the larger dynamic range,the signal S2, which is obtained by converting the input signal S1having the level Ldr into the analog signal, is output in a level Lahigher than the level Ldr as shown in the figure.

In this case, even if the signal S2 is input to the A/D converter 21,since the level of the signal S2 exceeds the dynamic range of the A/Dconverter 21, the data value of a signal output from the A/D converter21 overflows.

Further, FIG. 8C shows a case in which the dynamic range (maximum outputlevel) of the D/A converter 12 in the DSP 1 is smaller than the dynamicrange (maximum input level) of the A/D converter 21 of the signalprocessing block 4 as a relation to the dispersion of error.

In this case, since the D/A converter 12 has the smaller dynamic range,the signal S2, which is obtained by converting the input signal Sihaving the level Ldr into the analog signal, is output in a level Lbsmaller than the level Ldr.

The signal S2 has a small level in correspondence to a difference oflevels Ldr−Lb with respect to the dynamic range of the D/A converter 12regardless that the level of the signal S2 must be originally Ldr. Thatis, the dynamic range cannot be sufficiently secured.

As described above, the dispersion of error of the cells of the D/Aconverters and the A/D converters appears in a state that the dynamicrange is made improper as described above, this state appears as aphenomenon, for example, deterioration of solarization.

DISCLOSURE OF THE INVENTION

Accordingly, a signal processing device of the present invention isarranged as described below in consideration of the problems describedabove.

A signal processing device according to the present invention comprisesa first digital signal processing block and a second digital signalprocessing block.

The first digital signal processing block comprises a first gainadjustment means to which a digital signal subjected to predetermineddigital signal processing is input and from which the digital signal isoutput after a gain according to a set gain value is given to thedigital signal and a first digital to analog conversion means forconverting the digital signal output from the first gain adjustmentmeans to an analog signal and outputting the analog signal from thefirst digital signal processing block.

The second digital signal processing block comprises an analog todigital conversion means for converting the analog signal output fromthe digital to analog conversion means of the first digital signalprocessing block to a digital signal, a digital signal processing meansfor subjecting the digital signal output from the analog to digitalconversion means to predetermined digital signal processing, a secondgain adjustment means to which the digital signal output from thedigital signal processing means is input, from which the digital signalis output after a gain according to a set gain value is given to thesignal, and to which gain sensitivity lower than that of the first gainadjustment means is set, and a second digital to analog conversion meansfor converting the digital signal output from the second gain adjustmentmeans to an analog signal and outputting the analog signal from thesecond digital signal processing block.

In the above arrangement, the first digital to analog conversion meansand the analog to digital conversion means are set such that a relation,in which the minimum value within the range of dispersion of the errorsof the signal level in the first digital to analog conversion means isequal to or larger than the maximum value within the range of dispersionof the errors of the signal level in the analog to digital conversionmeans.

Further, the signal processing device comprises a detection means fordetecting the level value of the digital signal output from the secondgain adjustment means, a first gain set means for setting a gain valueto the first gain adjustment means such that the level value detected bythe detection means is set to a maximum value within the range less thea prescribed value in a state that a signal whose level is treated as amaximum value in the first digital signal processing block is input tothe first gain adjustment means, and a second gain set means for settinga gain value to the second gain adjustment means such that the levelvalue detected by the detection means is set to a maximum value withinthe range equal to or less than the prescribed value in a state that asignal whose level is treated as a predetermined maximum value is inputto the first digital signal processing block after the gain value is setby the first gain set means.

Further, a signal processing method is arranged as described below.

First, the signal processing method of the present invention executesfirst digital signal processing and second digital signal processing.

The first digital signal processing comprises a first gain adjustmentprocedure to which a digital signal subjected to predetermined digitalsignal processing is input and which gives a gain according to a setgain value and a first digital to analog conversion procedure forconverting the digital signal obtained by the first gain adjustmentprocedure to an analog signal and using the analog signal as an outputfrom the first digital signal processing.

The second digital signal processing comprises an analog to digitalconversion procedure for converting the analog signal obtained by thedigital to analog conversion procedure included in the first digitalsignal processing into a digital signal, a digital signal processingprocedure for subjecting the digital signal obtained by the analog todigital conversion procedure to predetermined digital signal processing,a second gain adjustment procedure to which the digital signal obtainedby the digital signal processing procedure is input and which gives again by gain sensitivity lower than the first gain adjustment procedureaccording to a set gain value, and a second digital to analog conversionprocedure for converting the digital signal obtained by the first gainadjustment procedure to an analog signal and outputting the analogsignal from the second digital signal processing unit.

The signal processing method further executes a set procedure forsetting a such a relation that the minimum value within the range ofdispersion of the errors of the signal level in a device correspondingto the first digital to analog conversion procedure is equal to orlarger than the maximum value within the range of dispersion of theerrors of the signal level in a device corresponding to the analog todigital conversion procedure, a detection procedure for detecting thelevel value of the digital signal obtained by the second gain adjustmentprocedure, a first gain set procedure for setting a gain value to thefirst gain adjustment procedure such that the level value detected bythe detection procedure is set to a maximum value within the range lessthe a prescribed value in a state that a signal whose level is treatedas a maximum value in the first digital signal processing is input tothe first gain adjustment procedure, and a second gain set means forsetting a gain value to the second gain adjustment procedure such thatthe level value detected by the detection procedure is set to a maximumvalue within the range equal to or less than the prescribed value in astate that a signal whose level is treated as a predetermined maximumvalue is input to the first digital signal processing block after thegain value is set by the first gain set procedure.

In the above respective arrangements, a digital signal processing systemis constructed by the first digital signal processing block (firstdigital signal processing) connected in series to the second digitalsignal processing block (second digital signal processing) as well as ananalog signal is transmitted therebetween as can be found from that theD/A conversion function and the A/D conversion function are interposedbetween both the blocks.

When a gain is to be set in the arrangement as described above, first,the minimum value within the range of dispersion of the errors of thesignal level of the D/A conversion function (first digital to analogconversion means/procedure) on the first digital signal processing blockside is set larger than the maximum value within the range of dispersionof the errors of the signal level of the A/D conversion function on thesecond digital signal processing block side. As a result, it can besecurely prevented that an input from the D/A conversion function on thefirst digital signal processing block to the A/D conversion function onthe second digital signal processing block falls short of a range.

Further, first, a gain value is set to the first gain adjustmentmeans/procedure such that the level value detected by the detectionmeans/procedure is set to the maximum value within the range less thanthe prescribed value in the state that the signal whose level is treatedas the predetermined maximum value is input to the first gain adjustmentmeans/procedure. After the gain value is set to the first gainadjustment means/procedure as described above, a gain value is set tothe second gain adjustment means/procedure such that the level valuedetected by the detection means/procedure is set to a maximum valuewithin the range equal to or less than the prescribed value in the statethat the signal whose level is treated as the predetermined maximumvalue is input to the first digital signal processing block likewise.

Here, the gains are set to the first and second gain adjustmentmeans/procedures based on the level value of the digital signal whosegain is set by the first and second gain adjustment means/procedures.With this operation, in the state that the gains are set as describedabove, a dynamic range as large as possible can be obtained regardlessthe dispersion of the errors of the signal levels in the D/A conversionfunction on the first digital signal processing block and in the A/Dconversion function on the second digital signal processing block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration example of an imagedisplay apparatus as an embodiment of the present invention.

FIGS. 2A, B, and C are views schematically showing a procedure examplefor setting a gain as a first embodiment.

FIG. 3 is a flowchart showing a processing operation for setting thegain as the first embodiment.

FIGS. 4A, B, C, and D are views schematically showing a procedureexample for setting the gain as the first embodiment.

FIG. 5 is a flowchart showing a processing operation for setting thegain as the first embodiment.

FIG. 6 is a block diagram showing a configuration example of an imagedisplay apparatus as conventional equipment provided with a DSP toexecute video signal processing.

FIG. 7 is a block diagram showing an arrangement of the image displayapparatus shown in FIG. 6 to which a signal processing block is newlyadded.

FIGS. 8A, B, and C are views explaining a phenomenon in which a dynamicrange is deteriorated due to dispersion of error of the signals of cellsof D/A converters and an A/D converter in the image display apparatusshown in FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an image display apparatus as an embodiment of the presentinvention. The image display apparatus includes an arrangement as asignal processing device based on the present invention. Although theembodiment is explained by exemplifying first and second embodimentsthat have a different gain setting procedure, the arrangement shown inFIG. 1 is common to the first and second embodiments.

A signal processing system of the image display apparatus shown in thefigure includes a DSP 1, a signal processing block 4, an LCD drivecircuit 2, and an LCD 3 when they are broadly classified.

The DSP 1, the signal processing block 4, the LCD drive circuit 2, andthe LCD 3 are mounted as independent chips or devices, respectively. Inthe above arrangement, the DSP 1 is connected to the signal processingblock 4 through terminals T1 and T2, the signal processing block 4 isconnected to the LCD drive circuit 2 through terminals T3 and T4, andthe LCD drive circuit 2 is connected to the LCD 3 through terminals T5and T6.

In this case, the interior of the DSP 1 is composed of a signalprocessing unit 11, a first GCA 13 (gain control amplifier), and a D/Aconverter 12. The signal processing unit 11 outputs a signal So (in aformat of a digital video signal), which is obtained by subjecting adigital video signal input to display an image to various requireddigital signal processing to the first GCA 13. The first GCA 13 sets again value G1 indicated by a control signal output from a microcomputer5, makes the gain of the input digital video signal (S0) variable, andoutputs it as a signal S1. Note that since the first GCA 13 is used toadjust the gain of a digital signal, it can be composed a multiplier andthe like used to, for example, a digital value.

The signal S1 output from the first GCA 13 is input to the D/A converter12 and converted into a signal S2 as an analog video signal which isoutput to the terminal T1. The signal S2 output to the terminal T1 isinput to the terminal T2 of the signal processing block 4.

The image display apparatus shown in FIG. 1 was previously composed of,for example, a DSP 1, an LCD 2, and an LCD 3. That is, it was composedby omitting the signal processing block 4. In this arrangement, aterminal T1 of the DSP 1 was connected to a terminal T4 of the LCD drivecircuit 2, thereby a signal S2 as an analog video signal output from theDSP 1 was input to the LCD drive circuit 2 as it was. A reason why theDSP 1 was arranged to output the analog video signal was based on thecondition that the output from the DSP 1 was input to the LCD drivecircuit 2.

The signal processing block 4 of the embodiment is a chip or a device asan external circuit additionally mounted to provide the previous imagedisplay apparatus with a novel predetermined signal processing function.That is, the signal processing block 4 is arranged to execute signalprocessing for realizing the novel predetermined signal processingfunction.

When it is intended to provide the previous image processing apparatuswith the novel predetermined signal processing function, it iscontemplated to redesign and manufacture the DSP 1 itself. However, thisrequires costs for developing and manufacturing it again.

For example, when addition of the novel signal processing function is asmall scale of modification in an overall system of the image displayapparatus, an effect resulting from the addition of the signalprocessing function may fail to match the costs of manufacturing andmounting the DSP 1 again and may be disadvantageous in cost. In thiscase, it is advantageous to additionally provide an external circuithaving the novel signal processing function with the previousarrangement. The embodiment is applied to this case, and the signalprocessing block 4 is additionally mounted on the arrangement of theprevious image display apparatus.

When the external circuit is composed of an analog circuit for executingthe video signal processing, a disadvantage arises in that a circuitsize and dispersion of a signal level increase. Accordingly, it is alsopreferable to arrange the external circuit to execute the digital signalprocessing. From the point of view described above, the signalprocessing block 4 is also arranged to execute the digital signalprocessing. That is, the signal processing block 4 is also arranged as asingle chip or a single device.

Although the signal processing block 4 executes the digital signalprocessing as described above, the video signal (S2) input from theterminal T1 of the DSP 1 is an analog format signal. The signalprocessing block 4 reconverts the analog video signal (S2) input fromthe terminal T2 into a digital video signal (S3) by the A/D converter 21and inputs it to a signal processing unit 22.

The signal processing unit 22 subjects the digital video signal (S3)input thereto to digital signal processing that corresponds to at leastthe novel signal processing function and outputs it as a signal S4. Thesignal S4 is input to a second GCA 24.

The second GCA 24 gives a gain, which is set according to a gain valueG2 indicated by the microcomputer 5, to the digital video signal (S4)input thereto likewise the first GCA 13 explained above and outputs itas a signal S5. Note that the second GCA 24 can be also composed of amultiplier and the like. However, in order to set the gains by the firstGCA 13 and the second GCA 24 in a manner described below, the first GCA13 has a gain sensitivity larger than that of the second GCA 24.

The digital video signal (S5) output from the second GCA 24 is input tothe D/A converter 23. The digital video signal (S5) is branched andinput also to the microcomputer 5.

When the LCD drive circuit 2 receives the video signal output from thesignal processing block 4, an analog signal is input to the LCD drivecircuit 2. Thus, in the signal processing block 4, the D/A converter 23converts the digital video signal (S5) input thereto into the analogvideo signal and inputs it to the terminal T4 of the LCD 2 through theterminal T3.

The LCD drive circuit 2 creates a drive signal for driving the LCD 3 fordisplay based on the analog video signal input thereto and inputs it tothe terminal T6 of the LCD 3 through the terminal T5.

The LCD 3 drives pixel cells in response to the drive signal inputthereto. With this operation, the LCD 3 displays an image according tothe video signal.

The microcomputer 5 is composed of a CPU (central processing unit), ROM,RAM, and the like, and the image display apparatus is controlled in, forexample, such a manner that the CPU executes a program installed on andstored in the ROM. In the embodiment, the microcomputer 5 adjusts gainsof the first GCA 13 and the second GCA 24 as described below.

In the image display apparatus arranged as shown in FIG. 1, the cells ofthe three sets of the D/A converters and A/D converters are disposed inseries in a signal processing system. The errors of the signal inputlevels of the cells of the D/A converters or A/D converters aredispersed with respect to a rated level.

More specifically, as to an input, an error occurs in such a manner thateven if “A” is set as a maximum allowable level (data value) determinedin a specification, actually, a level larger than “A” (data value) canbe input, a level (data value) smaller than “A” is set as an actualmaximum allowable level, or when “A” is input actually, a level isexceeded (overflows). Further, as to an output, an error occurs in sucha manner that even if a maximum output level (data value), whichresponds to a maximum level input signal, is set to “B” in thespecification, an output is actually made in a level larger or smallerthan the level B. Further, an amount of error of the input/output levelsis dispersed in the respective cells.

It is as described above that the dynamic range of the video signal ismade improper by the errors and the dispersion thereof.

In the embodiment, the first and second GCAs 13 and 24 are provided andfurther the gains thereof are set such that the dynamic range of thevideo signal is made proper regardless that the cells of the D/Aconverters and the A/D converters disperse.

Note that the gains are set at, for example, an adjustment step of amanufacturing process, and, fundamentally, when the gains are set once,gain values at the time are fixedly set thereafter. However, timing atwhich the microcomputer 5 sets the gains is not particularly limited,and, for example, it may be set every time a power supply is set up, atevery predetermined number of times the power supply is set up, or atevery predetermined intervals. When the gains are set in a chance at apredetermined frequency after shipment from a factory, the change ofdispersion of signal levels that is caused by, for example,deterioration with age and any other reasons can be coped with.

FIGS. 2A, B, and C schematically show a procedure as a first embodimentfor setting the gains to the first and second GCA 13 and 24 in theembodiment.

As described above, the signals levels of the D/A converter 12 in theDSP 1 and the A/D converter 21 in the signal processing block 4 havedispersed errors. Further, the range of dispersion of the errors, thatis, the maximum and minimum values of the errors of each device ispreviously determined in a specification. Further, the range ofdispersion of the errors (maximum value/minimum value) can be variablyset according to a constant of an element such as an eternal resistorand the like.

In the first embodiment, before the gains are adjusted actually, therelation between the range of dispersion of the errors of the D/Aconverter 12 and that of the A/D converter 21 is set as follows as apreparation step.

More specifically, first, as shown in FIG. 2A, the range of dispersionof the error of the D/A converter 12 can be shown by a maximum valueL1max and a minimum value L1min. Further, the range of dispersion of theerror of the A/D converter 21 is also shown by a maximum value L2max anda minimum value L2min. Then, as shown in FIG. 2A likewise, the minimumvalue of the D/A converter 12 is set equal to or larger than the maximumvalue L2max of the A/D converter 21 (or to a value equal to or largerthan the maximum value L2max).

After the gain is set as described above, in the first embodiment, adata value, which corresponds to a level that is prescribed as a maximumsignal level to be processed by the DSP 1, is set to the signal outputfrom the signal processing unit 11, that is, to the signal SO input tothe first GCA 13 as a signal source for adjustment executed thereafter.In, for example, the first embodiment, a signal 100IRE, whichcorresponds to a so-called white level, is used as a signal of the levelLs1.

Further, in the gain adjustment executed thereafter, a gain of one timeis set to the first and second GCAs 13 and 24 as an initial value.

In a state that the gain values G1, G2 of the first and second GCAs 13and 24 are set to the initial value, first, since the signal SO outputfrom the signal processing unit 11 of the DSP 1 can be regarded as thesame signal as the signal S1 input from the first GCA 13 to the A/Dconverter 21, the signal S1 also has the level Ls1 as shown in FIG. 2A.The level of the signal S2, which is obtained by converting the signalS1 into the analog signal by the D/A converter 12, is not made equal toor smaller than the maximum value L2max even if the amounts ofdispersion of the errors of the input to and the output from the D/Aconverter 12 is minimized. This is because a minimum value, which can beemployed by the signal S2, is the minimum value L1min of the range ofdispersion of the error of the D/A converter 12.

That is, when the level of the signal S1 input to the D/A converter 12is set to a maximum value allowed by the DSP 1, the signal S2 input tothe A/D converter 21 securely overflows depending on the range ofdispersion of errors set to the D/A converter 12 and the A/D converter21 shown in FIG. 2A (however, this is based on that the gain value ofthe first GCA 13 is set to one time). When this is analyzed from aninverse standpoint of view, the signal S2 is set such that it is notmade equal to or smaller than the actual allowable maximum input levelof the A/D converter 21 when the input signal S1 is set to an allowablemaximum value. That is, the output from the D/A converter 12 isprevented from being input to the A/D converter 21 in an insufficientrange state.

When the range of the S2 is insufficient when it is input to the A/Dconverter 21, the insufficient range cannot be recovered even if a gainis increased by the second GCA 24 located behind the A/D converter 21.Although the signal S2 is converted into the digital video signal S3 bythe A/D converter 21, the signal S3 includes a signal level error due tothe dispersion of error of the A/D converter 21. The signal S3 is inputto the second GCA 24 as the signal S4 through the signal processing unit22. It is assumed here that no signal level is changed as a result ofthe digital signal processing executed by the signal processing unit 22.More specifically, it is assumed that the gain value of the signalprocessing unit 22 is one time. Further, since the gain value of thesecond GCA 24 is one time, it can be assumed that the signals S4 and S5are the same signal. Accordingly, in this case, the signals S5 and S3can be regarded as the same signal.

The signal S3 is a signal which is digitized by the A/D converter 21 andoverflows. Accordingly, the signal S3 is set to a state that it is fixedto the maximum level (Ldr) of the dynamic range that is determineddepending on the actual dispersion of errors of the A/D converter 21within the range of dispersion of errors of the A/D converter 21(between the maximum value L2max and the maximum value L2min).

At the time, the signal S5 also has the same level as the signal S3. Asshown in FIG. 1, the signal S5 is also input to the microcomputer 5. Themicrocomputer 5 executes control processing for gain adjustment executedthereafter based on the level (data value) of the signal S5.

In the initial state, the signal S5 is fixed to the level Ldr asdescribed above, which means that a state that the signal overflows iscreated.

To adjust the gain by the microcomputer 5, first, the gain value G1 tobe set to the first GCA 13 is reduced until the level of the signal S5being input is reduced to a value equal to or less than level Ldr whilemonitoring the signal S5. Note that the gain value G1 is controlled bythe microcomputer 5 which outputs a control signal for indicating thegain value G1. Further, to describe for the purpose of confirmation, thelevel Ls1, which is prescribed maximum, is kept to the signal S0 inputto the first GCA 13 thereafter.

FIG. 2B shows how a gain value is set to the first GCA 13 describedabove.

More specifically, the level of the signal S1, which is output from thefirst GCA 13 and input to the D/A converter 12, is reduced by reducingthe gain value of the first GCA 13 from the initial value. Incorrespondence to the reduction of the signal S1, the level of thesignal S2, which is output from the D/A converter 12 and input to theA/D converter 21, is also reduced. However, in a state that the level ofthe signal S2 is larger than the level Ldr that is the maximum value ofthe dynamic range DR of the A/D converter 21, the signal S2 becomes anexcessive input in the A/D converter 21 and overflows therein. At thetime, it is detected that the signal S5 is fixed to the level Ldr.

As described above, since the signal S5 overflows as long as the levelthereof is fixed to the level Ldr, the microcomputer 5 controls thefirst GCA 13 to reduce the gain value set thereto.

When the gain value is reduced as described above, the signal S5 (thesignal S3 output from the A/D converter 21) is set to a value smallerthan the level Ldr for the first time. At the time, the gain value setto the first GCA 13 is made to a gain value optimum to the first GCA 13.More specifically, a state that a maximum level to the dynamic range DRis input can be obtained within a range in which no overflow (saturationof level) occurs behind the first GCA 13. Thereafter, the gain value setto the first GCA 13 at the time is fixedly set to the first GCA 13.

After the gain value is set to the first GCA 13 as described above, again is set to the second GCA 24. Setting of the gain to the second GCA24 begins from the state that the gain value has been set to the firstGCA 13.

As described above, the sensitivity of the first GCA 13 is set higherthan that of the second GCA 24, which means that, when the sensitivityis regarded as an amount of change of the output level of a signal inresponse to an amount of change of the same gain value having been set,the amount of change of the output level of the first GCA 13 is largerthan that of the second GCA 24, in other word, which means that theresolution of the change of an output level in response to the change ofthe gain value is larger in the second GCA 24 than in the first GCA 13.That is, in the video signal processing system shown in FIG. 1, thefirst and second GCAs 13 and 24 undertake a separate role in that theformer sets a rough adjustment gain and the latter sets a fineadjustment gain.

From what has been described above, in the state that the gain value ofthe first GCA 13 is set, the signal S5 is set to a level smaller thanthe maximum level Ldr of the dynamic range DR as shown in FIG. 2B.However, since the resolution when the gain is set to the first GCA 13is low, the difference between the level of the signal S5 and the levelLdr may be relatively large.

However, the resolution when the gain of the second GCA 24 is set isrelatively higher than that of the first GCA 13. Accordingly, it ispossible to adjust the difference between the level of the signal S5 andthe level Ldr as small as possible by making the level of the signal S5near to the level Ldr by setting the gain to the second GCA 24. Withthis operation, a maximum input level can be made more near to thedynamic range DR within a range in which no overflow (saturation oflevel) occurs. That is, the dynamic range as a signal itself can be moreimproved. The gain of the second GCA 24 is set for this purpose.

When the gain is actually set to the second GCA 24, the microcomputer 5controls the second GCA 24 to increase the gain value to be set to thesecond GCA 24 while monitoring the level of the signal S5. The gainvalue G2 is also set to the second GCA 24 by outputting a control signalfor indicating the gain value G2 by the microcomputer 5.

The gain is set to the second GCA 24 as shown in FIG. 2C.

The level of the signal S5 as the output from the second GCA 24 isincreased in response to the gain value of the second GCA 24 set to ahigher value as described above. To describe for the purpose ofconfirmation, since the resolution of the second GCA 24 to the change ofoutput level thereof is higher than that of the first GCA 13, the amountof change of the level of the signal S5 at, for example, every one stepis smaller than that of the first GCA 13.

Then, at a certain step, the signal S5 reaches a level that is regardedas the same level as the maximum level Ldr of the dynamic range DR asshown in FIG. 2C. This state corresponds to that a fine adjustment iscompleted to the gain set as described above, thereby a maximum dynamicrange can be conceptually secured within the range of level in which nooverflow occurs. However, actually, an overflow approximately occurs inthe state that the level of the signal S5 perfectly agrees with thelevel Ldr, which is actually not preferable. To cope with this problem,in actual processing, the gain value of the second GCA 24 is set smallerthan the state that the level of the signal S5 agrees with the level Ldrso that the level of the signal S5 is set smaller than the level Ldr bythe gain value of the one step. Thereafter, the gain value set to thesecond GCA 24 as described above is fixedly set to the second GCA 24.

A processing operation, which is executed by the microcomputer 5 (CPU)according to the gain setting procedure explained by FIGS. 2A, B, and C,is shown in a flowchart of FIG. 3. Note that when the processing shownin the figure is executed, the relation between the minimum value L1minwithin the range of dispersion of the errors of the D/A converter 12 andthe maximum value L2max within the range of dispersion of the errors ofthe A/D converter 21 is already set. Further, the initial value (forexample, the gain value corresponding to one time) is set to the gainvalues G1 and G2 of the first and second GCAs 13 and 24, respectively.

In the processing shown in the figure, first, data for maximizing thesignal level on the DSP side is created as an input signal at step S101.More specifically, as an example, the signal processing unit 11 iscontrolled such that the signal S0, which is output from the signalprocessing unit 11 of the DSP 1 and input to the subsequent signalprocessing system is made to the digital video signal having the level100IRE as described above. With this operation, the initial stateexplained with reference to FIG. 2A can be obtained. That is, in thesystem in which the signal S0 is processed and set to the signal 5, astate that a signal overflows (is set to an excessively large level) issecurely obtained.

The microcomputer 5 captures the data value (level) VS5 of the signal S5at next step S102. The level of the signal S5 is monitored by theprocessing.

At next step S103, it is determined whether or not VS5<Vdr isestablished as to the data value VS5 of the signal S5 captured at stepS102 and a preset prescribed value Vdr.

As described with reference to FIGS. 2A, B and C, in the initial state,the level of the signal S5 is fixed to the maximum level Ldr of thedynamic range DR and is equal to the level Ldr. The prescribed value Vdris fundamentally set to a data value corresponding to the level Ldr.Actually, however, the prescribed value Vdr may be set to an arbitrarypredetermined value smaller than the level Ldr in consideration that anoptimum dynamic range can be secured according to the specifications andthe like of the chips and the devices of the DSP 1 and the like.

When the relation VS5<Vdr is not established at step S103, that is, whena negative result of determination is obtained because a relation ofVS5≧Vdr is established, it can be said that a state of overflow stilloccurs.

To cope with this problem, the process goes to step S104 at which thegain value G1 to be set to the first GCA 13 is decremented by one step.As a result of the processing, the level of the signal S1 output fromthe first GCA 13 is reduced by an amount corresponding to the gain valuedecremented by the one step. On the completion of the processing at stepS104, the process returns to step S102. As described in FIG. 2B, anoperation for reducing the gain value to be set to the first GCA 13until no overflow occurs in the signal can be obtained by the processingflow from step S102 to step S104 through step S103.

When it is assumed that an affirmative result of determination isobtained because the relation VS5<Vdr is established at step S103, thestate that no overflow occurs can be obtained for the first time in thesignal processing system from the D/A converter 12 to which the signalS1 is input to the second GCA 24 from which the signal S5 is output.That is, the gain value G1 is properly set to the first GCA 13. In thiscase, the process goes to processing for setting the gain to the secondGCA 24 at step S105 and subsequent steps. Thereafter, the gain value G1set to the first GCA 13 is not changed, thereby the gain value G1 of thefirst GCA 13 is fixedly set.

To set the gain to the second GCA 24, first, at step S105, the gainvalue G2 is incremented by one step. With this operation, the level ofthe signal S5 output from the second GCA 24 is increased in response tothe gain value G2 increased by one step.

At next step S106, the data value VS5 of the signal S5 is capturedlikewise previous step S102. Then, at subsequent step S107, it isdetermined whether or not the relation VS5≧Vdr is established as to thedata value VS5 and the prescribed value Vdr. When the relation VS5≧Vdris not established and a negative result of determination is obtainedbecause the data value VS5 is smaller than the prescribed value Vdr, thegain of the second GCA 24 can be set to a large value. In this case, theprocess goes to step S108, increments the gain value G2 by one step, andreturns to the processing at step S106. In the flow of processing fromstep S106 to step S108 through step S107, the gain is finely adjusted sothat a maximum dynamic range can be forcibly obtained.

When the affirmative result is obtained at step S107, it is assumed herefor the first time that the signal S5 has reached the same level as themaximum level Ldr of the dynamic range DR. In this case, the processgoes to processing at step S109.

At step S109, the gain value G2 is decremented by one step.

As described above, the processing is executed to reduce the level ofthe signal S5 by the gain value of one step so that a state that anyoverflow does not securely occur can be obtained. On the completion ofthe processing at step S109, the gain setting processing shown in thefigure is finished. With this operation the gain value of the second GCA24 is also fixedly set to the final value thereafter.

Incidentally, what has been explained with reference to FIGS. 2A, B, andC is based on that the gain (signal processing gain) given to the signalby the signal processing by the signal processing unit 22 in the signalprocessing block 4 is one time, and thus the gain control in the signalprocessing system is equivalent to that the signal processing unit 22 ispassed.

However, as a matter of fact, it is also possible depending on a type ofsignal processing that a gain is given to a signal after it is processedand thus the level of the signal itself changes. Accordingly, the signalprocessing unit 22 may employ an arrangement for executing signalprocessing for giving a gain to a signal.

Therefore, next, how a gain is set in the embodiment when a signalprocessing unit 22 is arranged to give a signal processing gain otherthan one time to a signal to be processed will be explained as a secondembodiment.

FIGS. 4A, B, and C show a procedure example for setting the gain as thesecond embodiment.

Also in this case, as the relation between the range of dispersion ofthe errors of a D/A converter 12 and that of an A/D converter 21, theminimum value L1min of the D/A converter 12 is set equal to or largerthan the maximum value L2max of the A/D converter 21 or to a valuelarger than the maximum value L2max as a preparation step as shown inFIG. 4A.

Further, a data value corresponding to the level Ls1 (for example,100IRE) that is prescribed maximum as a signal level treated by a DSP 1is set to the signal S0 input to a first GCA 13 likewise. Further, again of one time is set to both the first GCA 13 and a second GA as aninitial value. With this operation, a state that a signal securelyoverflows can be obtained in a state that the first GCA 13 and thesecond GCA initially have the gain of one time (equivalent to apassing-through state), respectively.

Further, it is assumed that the gain value (xn) of the signal processinggain in the signal processing unit 22 is set to n=0 to 2. In this case,a maximum gain value is set to 2 times. However, FIG. 4A shows a casethat the gain value of the signal processing gain in the signalprocessing unit 22 is set to 2 times that is a maximum value as arelation between the level of the S3 input to the signal processing unit22 and that of the signal S4 output from the signal processing unit 22.In this case, it is shown that when the signal S3 is has the maximumlevel Ldr of the dynamic range DR, the signal S4 has a level Lsp that istwice the level Ldr. Further, in this case, since the gain value G2 ofthe second GCA 24 is set to a value corresponding to the one time of theinitial value, the signal 5 output from the second GCA 24 has the samelevel as the signal S4.

Further, in this case, as an initial state, the gain value of the signalprocessing gain in the signal processing unit 22 is controlled to onetime (n=1) as shown in FIG. 4B. When the gain of the first GCA 13 is tobe set, the signal S4 input to the second GCA 24 must have the samelevel response as that of the signal S3 output from the A/D converter 21likewise the previous embodiment. At the time, when the gain value inthe signal processing gain of the signal processing unit 22 is a valueother than the one time, the level response of the signal S4 is set to alevel response different from that of the signal 3.

Thus, the signal S4 (S5) output from the signal processing unit 22 canbe set to the same level as that of the signal S3 input to th3 signalprocessing unit 22 as shown in FIG. 4B by setting the gain value of thesignal processing gain in the signal processing unit 22 to the one time.Note, at this time, since an overflow (excessive input) state occurslikewise the previous first embodiment, the signals S3, S4, and S5 arefixed to the level Ldr.

As described above, since the gain value of the signal processing gainof the signal processing unit 22 is set to the one time as describedabove, when the signal processing system shown in FIG. 1 is viewed inits entirety, the gain setting state is equivalent to the case explainedabove with reference to FIGS. 2A, B, and C.

In this state, the gain value G1 of the first GCA 13 is reduced from theinitial value until the level of the signal S5 is made smaller than thelevel Ldr as shown in FIG. 4 while monitoring the level (data value) ofthe signal S5 by a microcomputer 5. That is, the gain is set to thefirst GCA 13 likewise the explanation made with reference to FIG. 2B inthe previous first embodiment.

Subsequently, although a gain is set to the second GCA 24, the signalprocessing gain of the signal processing unit 22 located just in frontof the second GCA 24 must be taken into consideration when the gain isset. This is because, in this case, the dynamic range of a D/A converter23 in the same is set based on a maximum signal level when the signalprocessing gain of the signal processing unit 22 is set to a maximumvalue. Accordingly, the gain value of the second GCA 24 must be set suchthat the second GCA 24 can maximally make use of the dynamic range ofthe D/A converter 23.

For this purpose, when the gain of the second GCA 24 is to be set, thesignal processing gain of the signal processing unit 22 set to two timesas shown in FIG. 4D. That is, it is set to a maximum value.

With this operation, the signal S4 output from the signal processingunit 22 has a level twice the signal S3 input to the signal processingunit 22. In this case, since the gain of the first GCA 13 is set, thelevel of the signal S3 has a value smaller than, for example, themaximum level (prescribed value) Ldr of the dynamic range DR. Inresponse to the level of the signal S3, the level of the signal S4 has avalue that is smaller than the level Lsp that is just twice the maximumlevel Ldr of the dynamic range DR although it is near to the level Lsp.

After the above state is achieved, the microcomputer 5 increases thegain value G2 set to the second GCA 24 until the level of the signal S5is set equal to the level Lsp.

When the level of the signal S5 is set equal to the level Lsp, it can besaid that a state, in which a maximum dynamic range can be secured, isachieved within the range of level in which no overflow occursconceptually. In actual processing, however, the gain value of thesecond GCA 24 is set smaller than the state that the level of the signalS5 is set equal to level Ldr so that the level of the signal S5 is setsmaller than the level Ldr by the gain value of the one step to therebyprevent overflow from occurring actually.

A flowchart of FIG. 5 shows a processing operation executed by themicrocomputer 5 (CPU) according to the gain setting procedure explainedwith reference to FIGS. 4A, B, and C.

In the processings executed at S201 to S205 in the figure, theprocessings other than that executed at step S202 are the same as thoseexecuted at steps S101 to S104 of FIG. 3. As explained in FIG. 4B, theprocessing at step S202 is executed to set the level of the signal S4(S5) equal to the signal S3 when the gain of the first GCA 13 is set.

When an affirmative result of determination is obtained at step S204,the process goes to a processing sequence for setting the gain of thesecond GCA 24 at step S206 and subsequent steps, at which the gain ofthe first GCA 13 is set.

At step S206, the gain value of the signal processing gain of the signalprocessing unit 22 is set to a maximum value Gspmax. When the gain valueis treated here as a multiple number (n), which is used as the gain, asit is, Gspmax=2 is established in the examples of FIGS. 4A, B, C, and D.

Processings at steps S207 to S211 subsequent to step S206 are the sameas the processings at steps S106 to S109 of FIG. 3 corresponding to theprevious embodiment.

However, since the maximum value Gspmax is set as the gain value of thesignal processing unit 22, whether or not the following formula isestablished is determined to determine the relation between the datavalue VS5 of the signal S5 and the prescribed value Vdr at step S209.

Vs5≧Vdr×Gspmax

With this operation, the level of the signal S5 is set equal to thelevel Lsp (actually, the level is set smaller than the level Lsp by onestep by the processing at step S210) as described in FIG. 4D. Note thatFIG. 4D is an example of a case in which the data value corresponding tothe level Ldr is set to the prescribed value Vdr. As described above,when the processings up to step S211 are executed, the gains of thefirst and second GCAs 13 and 24 are set.

It should be noted that the present invention is by no means limited tothe arrangements of the embodiments explained up to now.

Further, the present invention can be also applied to a case in which aplurality of signal processing blocks are connected in parallel behindthe DSP 1. That is, after the gain is set to the first GCA 13 once asdescribed in the embodiment, the gain is sequentially set to the secondGCA in each of the signal processing blocks connected in parallel in therear stage.

Further, in, for example, the embodiment explained up to now, theexample in which the one set of the signal processing block 4 is addedto the DSP 1 as shown in FIG. 1. However, it is also contemplated toapply the present invention to an arrangement in which a signalprocessing block is further connected in series behind, for example, theDSP 1—the signal processing block 4.

Further, although the above embodiment exemplifies the image displayapparatus as equipment including the signal processing device based onthe present invention, a display device such as a plasma display, acathode ray display tube, and the like may be employed as the imagedisplay apparatus, in addition to the LCD. Further, various types ofdevices such as image recording equipment, a DVD (digital versatiledisc) player, and the like are known as equipment for executing digitalvideo signal processing, and the present invention can be applied to theequipment.

Further, although the embodiment exemplifies to set the gain to thevideo signal, it can be also applied to an arrangement for executing thedigital signal processing to signals having other formats such as anaudio signal and the like.

INDUSTRIAL APPLICABILITY

As described above, the present invention overcomes a problem in thatwhen signals of an analog signal format are input and output between twoblocks for executing digital signal processing, a dynamic range is madeimproper by the dispersion of errors of the signal levels in a D/Aconverter and an A/D converter disposed in the blocks, thereby it ispossible to provide, for example, a result of the reproduced output of asignal with excellent quality.

1. A signal processing device, comprising a first digital signalprocessing block and a second digital signal processing block, wherein:the first digital signal processing block comprises: first gainadjustment means to which a digital signal subjected to predetermineddigital signal processing is input and from which the digital signal isoutput after a gain according to a set gain value is given to thedigital signal; and first digital to analog conversion means forconverting the digital signal output from the first gain adjustmentmeans to an analog signal and outputting the analog signal from thefirst digital signal processing block, the second digital signalprocessing block comprises: analog to digital conversion means forconverting the analog signal output from the digital to analogconversion means of the first digital signal processing block to adigital signal; digital signal processing means for subjecting thedigital signal output from the analog to digital conversion means topredetermined digital signal processing; second gain adjustment means towhich the digital signal output from the digital signal processing meansis input, from which the digital signal is output after a gain accordingto a set gain value is given to the signal, and to which gainsensitivity lower than that of the first gain adjustment means is set;and second digital to analog conversion means for converting the digitalsignal output from the second gain adjustment means to an analog signaland outputting the analog signal from the second digital signalprocessing block, the first digital to analog conversion means and theanalog to digital conversion means are set such that a relation, inwhich the minimum value within the range of dispersion of the errors ofthe signal level in the first digital to analog conversion means isequal to or larger than the maximum value within the range of dispersionof the errors of the signal level in the analog to digital conversionmeans, and the signal processing device further comprises: detectionmeans for detecting the level value of the digital signal output fromthe second gain adjustment means; first gain set means for setting again value to the first gain adjustment means such that the level valuedetected by the detection means is set to a maximum value within therange less the a prescribed value in a state that a signal whose levelis treated as a maximum value in the first digital signal processingblock is input to the first gain adjustment means; and second gain setmeans for setting a gain value to the second gain adjustment means suchthat the level value detected by the detection means is set to a maximumvalue within the range equal to or less than the prescribed value in astate that a signal whose level is treated as a predetermined maximumvalue is input to the first digital signal processing block after thegain value is set by the first gain set means.
 2. A signal processingdevice according to claim 1, wherein: when the gain of the digitalsignal is changed, the first gain set means inputs a signal whose levelis treated as the predetermined maximum value to the first digitalsignal processing means as well as the gain value is set to the firstgain set means such that the level value detected by the detection meansis set to a maximum value within the range less than the prescribedvalue in a state that the gain value is set to a maximum gain value inthe digital signal processing means; and the second gain set meansinputs a signal whose level is treated as a predetermined maximum valueto the first digital signal processing block after a gain value is setby the first gain set means as well as sets a gain value to the secondgain adjustment means such that the level value detected by thedetection means is set to a maximum value within the range equal to orless than the prescribed value in a state that the gain value is set toone time in the digital signal processing means.
 3. A signal processingmethod of executing first digital signal processing and second digitalsignal processing, wherein: the first digital signal processingcomprises: a first gain adjustment procedure to which a digital signalsubjected to predetermined digital signal processing is input and whichgives a gain according to a set gain value; and a first digital toanalog conversion procedure for converting the digital signal obtainedby the first gain adjustment procedure to an analog signal and using theanalog signal as an output from the first digital signal processing, thesecond digital signal processing comprises: an analog to digitalconversion procedure for converting the analog signal obtained by thedigital to analog conversion procedure included in the first digitalsignal processing into a digital signal; a digital signal processingprocedure for subjecting the digital signal obtained by the analog todigital conversion procedure to predetermined digital signal processing;a second gain adjustment procedure to which the digital signal obtainedby the digital signal processing procedure is input and which gives again by gain sensitivity lower than the first gain adjustment procedureaccording to a set gain value; and a second digital to analog conversionprocedure for converting the digital signal obtained by the first gainadjustment procedure to an analog signal and outputting the analogsignal from the second digital signal processing unit, wherein thesignal processing method further executes: a set procedure for setting asuch a relation that the minimum value within the range of dispersion ofthe errors of the signal level in a device corresponding to the firstdigital to analog conversion procedure is equal to or larger than themaximum value within the range of dispersion of the errors of the signallevel in a device corresponding to the analog to digital conversionprocedure; a detection procedure for detecting the level value of thedigital signal obtained by the second gain adjustment procedure; a firstgain set procedure for setting a gain value to the first gain adjustmentprocedure such that the level value detected by the detection procedureis set to a maximum value within the range less the a prescribed valuein a state that a signal whose level is treated as a maximum value inthe first digital signal processing is input to the first gainadjustment procedure; and a second gain set means for setting a gainvalue to the second gain adjustment procedure such that the level valuedetected by the detection procedure is set to a maximum value within therange equal to or less than the prescribed value in a state that asignal whose level is treated as a predetermined maximum value is inputto the first digital signal processing block after the gain value is setby the first gain set procedure.